A GRISM is a transmission grating coupled to prism. In comparison with a more typical flat grating, a GRISM enables the use of higher spatial frequency and hence yields higher angular dispersion. Such devices therefore find utility in various applications, including spectrometers, telecommunications, and others. Conventionally, fused silica is used both as the substrate and cover plate for transmission gratings because of its low coefficient of thermal expansion and resulting thermal stability of the grating spatial frequency. However, the thermal coefficient of refractive index associated with fused silica is quite high, such that it may be unsuitable for use as a prism, otherwise more than offsetting its low thermal expansion coefficient where significant prism power is employed. Thus, a solution to this problem is desirable.